The disclosure generally relates to a semiconductor device with a charge carrier compensation structure in a semiconductor body and to a method for its production. The semiconductor body includes drift zones of a first conduction type with a semiconductor material applied epitaxially in epitaxial growth zones. The semiconductor body further includes charge compensation zones of a second conduction type complementing the first conduction type, which are provided with a semiconductor material applied in epitaxial growth zones.
Semiconductor devices of this type are applied to a semiconductor substrate in a multi-epitaxial process, the aim being the production of a high-blocking power transistor with a minimal on resistance. In order to reduce a specific on resistance, the step width between the drift zones and the charge compensation zones is kept to a minimum to permit the use of a very high doping level. This is however counteracted by the tendency towards a lateral spreading of the compensation regions, which are introduced into the epitaxial growth zones by ion implantation and are spread both vertically and laterally by diffusion. In this context, vertical outdiffusion is required for the formation of coherent compensation regions. Lateral outdiffusion, however, is an undesirable side effect.
The lateral spreading of the charge compensation regions makes a minimum step width between drift zones and charge compensation zones difficult to achieve and therefore has to be kept to a minimum. Another factor which counteracts the reduction of this step width is the fact that the typical current density in the device automatically increases as the step width is reduced. This means that in an avalanche situation the modulation of the space charge through the charge carriers becomes increasingly serious as the step width is reduced.
The reduction of the step width further strengthens the influence of common process variations, making the production of avalanche-proof and therefore robust compensated devices difficult. The most widespread process in the production of a compensated device is the homogeneous introduction of a doping material during the epitaxial process followed by the masked selective implantation of a complementary doping material using masks. In this technology, the reduction of the step width is restricted by the fact that the masked implanted doping material is in the diffusion process incorporated into the homogeneously doped epitaxial growth zone to virtually the same degree both laterally and vertically. As a result, the shape of the p-n junction between the compensation regions has bulges in the lateral direction in each epitaxial growth zone.
To avoid such bulges, both types of doping material can be introduced by masked implantation, which however is a cost-intensive process. Identical diffusion coefficients for both doping materials result in similar equiconcentration lines for both types of doping material. In addition, the shape of the p-n junction between the compensation regions becomes nearly vertical with very few bulges. If, however, the diffusion process is excessively long, the doping materials increasingly diffuse into the complementary doping material region and there neutralize the other doping material. This means that considerably more doping material has to be introduced for a preset on resistance than is available for current flow in the drift zones at the end of the process. More doping material, however, automatically leads to increased fluctuations in the production process. A product of this type therefore becomes increasingly difficult to produce for increasing diffusion periods, because absolute misdoping at, for example, a dose error of 2% increases in proportion to the implanted dose in the implantation process.
In addition, semiconductor devices produced using the multi-epitaxial process exhibit a marked electric field strength ripple in the vertical direction in the middle of the drift zone as a result of the masked implantation of both types of doping material. The adjacent arrangement of drift zones and compensation zones moreover automatically produces a transverse magnetic field which drives generated electron precisely into this middle region of the drift zone. There the generated electrons have to pass through the relative field maximum values. This generates additional charge carriers.
To reduce this effect, a complementary doping can be introduced into a homogeneous doping for the drift zone using a mask in the lower region of the charge carrier compensation structure near the drain, while in the region near the source a masking doping of the drift zone is introduced into a complementary and homogeneously applied background doping. If field peaks are to be avoided in the transitional region between the regions near the drain and near the source, however, an additional epitaxial growth zone with a reduced concentration of doping material is required, which increases the on resistance for the device as a whole.